It costs so much to apply for US citizenship — $725 — that a top city official wants local taxpayers to pick up the $20.7 million tab for up to 35,000 poor applicants.

Comptroller Scott String­er suggested setting up a public-private partnership to help cover the application fee for an estimated 670,000 New York City residents eligible for naturalization.

But until that’s established, he suggested the city come up with the money for 35,000 of the 180,000 earning $61,260 or less for a family of three.

“Now, more than ever, we need to embrace bold, innovative strategies to protect our immigrant communities,” Stringer said at a press conference in Battery Park, with the Statue of Liberty in the background.

“If we want to fight back against President Trump, this is a smart, common-sense, policy-driven strategy that all New Yorkers can help to support.”

Officials said an impending price boost in the form-filing fee in 2008 — from $400 to $675 — sparked an 89 percent surge in citizenship applications, many from people seeking to pay the lower fee.

After the higher pricing was implemented, applications decreased by more than half, the officials said.

The Mayor’s Office of Immigrant Affairs issued a statement saying it looked forward to “receiving his letter and further discussing our NYCitizenship program and MOIA’s other work to create pathways to citizenship for more New Yorkers.”